Cationic electrodeposition coating compositions have been used for undercoating bodies and parts of automobiles, and required to form coating films with high corrosion resistance. The coating films need to be sufficiently cured at a predetermined baking temperature to achieve the high corrosion resistance. Dibutyltin compounds are generally used as a curing catalyst for lead-free cationic electrodeposition coating compositions. For example, dibutyltin oxide, which is usable as a catalyst for cross-linking reaction of a cationic electrodeposition coating composition, is described in JP-A-5-65438. Further, a cationic electrodeposition coating composition containing an organotin compound is disclosed in JP-A-7-258586, and a cationic electrodeposition coating composition containing a dialkyltin aromatic carboxylic acid salt as a curing catalyst is disclosed in JP-A-2001-55538.
However, in general, the dibutyltin compounds are disadvantageously volatile. For example, surface temperature of electrodeposition coating films is raised to 150 to 180° C. in a process of baking the films, coating the film with an upper film of a chipping primer, an intermediate coating, etc., or baking the upper film. The dibutyltin compounds are volatilized from the surface of the electrodeposition coating films at such a high temperature, transferred into the adjacent upper film of the chipping primer or the intermediate coating, and thereby negatively affects the film performances or appearance of the finish coating film in some cases.